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Rotary Movements

post #1 of 23
Thread Starter 


I rarely start new posts, however, in light of the recent discussions concerning biomechanics in skiing I felt moved to do so.

I only have a couple points to make.

In summation, I think this is a good example of the rotary mechanism Joubert described three decades ago put into use on skis. The reason I term it in this manner is because the same mechanism is evident in the pivot slips demonstrated by Ric.

Add a little edge engagement to the pivot slip and you have a parallel turn.

A pretty good parallel turn to boot.

I was intrigued to observe the lines on the side of Bob's pant leg.

I also was intrigued to see the same backpedaling observed in the other montages that is so often associated with skiing moguls. The open parallel turns appear to have a "virtual bump" and that is simply because the skis are turned uphill.

For those who want to understand the role of rotary movements in steering.....here it is.
post #2 of 23
I thought it was a real bump....
post #3 of 23
RustyGuy:

Bear with me on this, because I'm trying to assimilate this clip (and Nolo's) with some of the ongoing themes here. Also, I'm most definitely not an instructor, so it's entirely possible that when I look at something, I'm not seeing what I'm supposed to.

Two specific practices that seem to come in for criticism here are narrow stance and unweighting.

Unwieghting... the clip you posted *seems* to have the skier doing some degree of what I would call unweighting. More so than Nolo's clip, anyway. Am I wrong?

Narrow stance... both of these clips show what seems like a narrower stance than what I've inferred would be recommended for *modern* technique. True or false? (I'd say they looked almost Harbian, if I were in a playful mood.)

A final question... is the skier in the clip above carving those turns?

Bob
post #4 of 23
Thread Starter 
Quote:
Originally posted by Bob Peters:
RustyGuy:

Bear with me on this, because I'm trying to assimilate this clip (and Nolo's) with some of the ongoing themes here. Also, I'm most definitely not an instructor, so it's entirely possible that when I look at something, I'm not seeing what I'm supposed to.

Two specific practices that seem to come in for criticism here are narrow stance and unweighting.

Unwieghting... the clip you posted *seems* to have the skier doing some degree of what I would call unweighting. More so than Nolo's clip, anyway. Am I wrong?

Narrow stance... both of these clips show what seems like a narrower stance than what I've inferred would be recommended for *modern* technique. True or false? (I'd say they looked almost Harbian, if I were in a playful mood.)

A final question... is the skier in the clip above carving those turns?

Bob
As we turn weight or pressure builds on the outside ski. A new turn is begun by releasing the old outside ski. The term "release" is merely flattening the old outside ski and beginning to turn the old outside tip in the direction of the new turn. In it's simplist form it is a blend of tipping and turning. In this case the bias towards rotary movement. It could be argued ad nauseum, however, let's call it 10% tipping and 90% turning.

The reason I began with the above is that the release is really a form of unweighting or relieving the built up pressure.

If you mean you see Bob with any sort of up-unweighting or down-unweighting I don't see it.

In fact I marvelled at how "quiet" his upper body remains. Keep in mind these are actually photo-montages or clips of video that have been in essence spliced together.

Bob does have a relatively narrow stance BECAUSE he has relatively narrow hips. He is a skinny guy. I think if his stance was any wider he would appear bow-legged.

I actually called Bob and recommended he re-arrange the photos and have his appear just after Ris's pivot slips. The idea being you take the mechanics of a pivot slip, add a degree of tipping, and you create a turn. Having said that the bias in these turns is towards rotary steering, thus, no they are nut carved.

What is important to note is the tail of the ski follows the tip of the ski. There is no tail pushing or tail displacement.
post #5 of 23
I too see what looks like some slight unweighting. I'm thinking that this may be the result of the "virtual bump".

As to stance width, I'd call it a "natural" stance rather than wide or narrow. For a slender guy, Bob seems to have plenty of seperation between his boots as his outer boot(s) seems to align with the outer hip(s). I don't know that this makes his stance "wide", but I certainly wouldn't refer to it as "narrow".
post #6 of 23
Thread Starter 
I was actually the camerman and it was on a groomed blue. I think some of what we are seeing is as a result of the editing process.
post #7 of 23
I'd let you "edit" my skiing, if you could promise it would look like that when you're done.
post #8 of 23
Quote:
Originally posted by Rusty Guy:
... the bias in these turns is towards rotary steering, thus, no they are nut carved.
Rusty, I can certainly see the rotary, but don't you think you're being a bit hard on Bob [img]tongue.gif[/img] [img]tongue.gif[/img]

Quote:
What is important to note is the tail of the ski follows the tip of the ski. There is no tail pushing or tail displacement.
On a more serious note! What would you think of the concept of carving with less than the full length of the ski? Say, barely more than what length is underfoot/underboot. Would that concept have any bearing in Bob's turns above? Thoughts?

Also, I don't see the unweighting ...I think the perception is a result of the clips being parsed together. That sequence is pretty smooth, but Bob is more fluid live and in person!
post #9 of 23
Thread Starter 
I guess I'm not sure what you mean by carving with less than the full length of the ski.
post #10 of 23
Rusty, I see a ton of rotation going on here, anticipation rotation to be precise.

Bob is developing a huge counter position at the end of the turn that acts as a coiled spring which pulls the legs/feet into compliance once unweighting occurs.

I see some unweighting here, a very subtle, minute, rebound triggering knee extension. The rebound is the mechanism that releases the spring, and initiates upper/lower body rotational harmony, which sets the new turn into motion.

Your right, these are not carved turns, they're steered. I'm sure they are a more controlled steer than this video projects, they look very tail tossy at turn completion here. The tails definitely do not follow the tips in these turns.

I was a little disappointed to see this. In Bob's thread he has them labeled as "skiing the slow line fast". I was under the impression that referred to carved turns.
post #11 of 23
Rusty,

This was something Ric got me working on in moguls, and, in that sequence you posted, it looks like Bob is doing the same thing ...without any moguls though. It was easy to see demonstrated ...I'll try to describe it.

For simplicity, lets assume a perfectly round shaped mogul, like a large ball cut in half. Imagine standing on the front side about 6" down from the top with your skis across the fall-line and the top of the mogul directly down the fall-line from the center of your balance point under your feet. As you're standing there on that sphere shaped mogul, the only contact point for your skis is right under your feet and the tips and tails are extending into the air. Now make a carved turn around the top of the mogul staying that same 6" down from the top all the way around. By employing the tipping and steering into the turn you described above ("...mechanics of a pivot slip, add a degree of tipping..."), you can carve this ridiculously small radius turn. Essentially your skis are only several inches long though, because the majority of your skis are floating in mid air .... they could be 215cm or blades, wouldn't make a bit of difference.

Does that make sense?

So my question above was basically, can the same thing be done on flats without the tip & tail of the ski off the snow? By employing the mechanics you describe in the sequence above, could the center 18" of Bob's skis be making a carved turn despite what the extreme ends may be doing?
post #12 of 23
Quote:
Originally posted by Rusty Guy:
I was actually the camerman and it was on a groomed blue. I think some of what we are seeing is as a result of the editing process.
Rusty,

Any chance of getting a bit of the actual footage, that might clear up some of the "montage" effect?
post #13 of 23
Quote:
Originally posted by cgeib:
you can carve this ridiculously small radius turn. Essentially your skis are only several inches long though, because the majority of your skis are floating in mid air .... they could be 215cm or blades, wouldn't make a bit of difference.

Does that make sense?

cgeib, it really doesn't work. You aren't actually carving that short turn, your steering it. It just steers very easily because the tip and tail are not there to impede the foot twist, so much so that it makes the steer very unrecognizable.

The small part of the ski in contact with the snow still is part of the whole ski and carries with it the same radius limitations. Only if the small section of ski in contact with the snow had an enhanced radius shape to it could you truly reduce the radius of a carved turn.
post #14 of 23
Thread Starter 
cgeib,

It does make sense and that was a great description. I can't post the footage for two reasons. Bob now has the disk and I don't yet have the expertise to transfer from camera, to laptop, to the web. I'll call him and ask him to put more footage on-line.

Ric would be in a better position to chime in here, however, I don't think it's applicable in this case because one cannot disengage the tail or tip of the ski in the manner you have described due to being on a sphere on the bump you describe. I think in the bump scenario, a very small turn can be made due to where it is being made. I can imagine cutting a basketball in half, putting it on a floor and in theory carving circles around it down to the floor.

Remember....I said in theory.

By the way. Every time your name is mentioned Bob says how well you were skiing the last time he saw you! I thought you'd like th hear that.

fastman,

I think Bob is in a better position to respond, however, I'll give it a shot.

Obviosly the rotation of his legs establishes counter. It may well create tension or the spring like effect you describe, however, I know from skiing with Bob on that day the triggering mechanism to start the next turn, was not the coiled spring pulling his feet into compliance, rather it is tipping the old outside/new inside foot in conjunction with eversion and lateral rotation. Right tip right to go right and left tip left to go left. Is there some coiling or tension inherently built up at the end of one turn? Sure. I guess what I am saying is the tension is so slight that it couls have been held in check and wasn't the triggering mechanism for the next turn.

It's just like Ric's pivot slips. He could stand in a slide or side slip until he seeks to rotate the old outside/new inside ski in the opposite direction.

Again, I hesitate to put words in Bob's mouth, however, I think the term unweighting is inappropriate. I'll get Bob to "weigh in" on this and personally unweight. I think weight transfer occurs more as a resultant in these turns not as an active movement. Unweighting infers weight transfer and that does not occur at turn initiation. This being the case, I would argue there is no active unweighting.

I disagree with the term "tail tossy". Perhaps it's the video. Watch how clearly Bob's feet continue moving forward. If the tail were being pushed or tossed the feet would appear in the video to stop as the heel is pushed out or the foot pushed out. If there is one thing Bob does really well in these type turns is have the tips of the skis moving in the intended direction of the turn, hence, pulling the tails in that direction as well.

Skiing the slow line as fast as you care to has nothing to do with carved vs skidded vs scarved. It has more to do with "line" and "intent" or offensive vs defensive movements. A skier in the first day of lessons can ski the slow line fast. The simple example is a gliding wedge vs braking wedge. It is a turn where the skier picks a point or line they intend to follow. The turn may involve gaining speed and eventually via turn shape may involve loosing speed as the turn goes uphill. That's the as fast as they care to part.
post #15 of 23
'What is important to note is the tail of the ski follows the tip of the ski. There is no tail pushing or tail displacement'

What?
post #16 of 23
Thread Starter 
Quote:
Originally posted by daslider:
'What is important to note is the tail of the ski follows the tip of the ski. There is no tail pushing or tail displacement'

What?
Just as in Jenn Metz's wedge christies, the tips are turn as opposed to the tails being pushed.

There is a very big difference.

Imagine if you were standing on skis and I merely came up to you, grabbed both ski tips, and pulled you by the tips and we completed a turn.

Akin to the manner the front wheels of a car pull a vehicle.
post #17 of 23
Quote:
Originally posted by Rusty Guy:
cgeib,

It does make sense and that was a great description. I can't post the footage for two reasons. Bob now has the disk and I don't yet have the expertise to transfer from camera, to laptop, to the web. I'll call him and ask him to put more footage on-line.
Wish I could take credit for the description, but it's my (hopefully accurate) recollection of what was described to me.

Hope ya can get that footage linked up!

Quote:

By the way. Every time your name is mentioned Bob says how well you were skiing the last time he saw you! I thought you'd like th hear that.
Yep [img]smile.gif[/img] , thanks. I think I made some headway on that countering we talked about in Nov. Still got a ways to go though...
post #18 of 23
Wow--good discussion, everyone! I agree that it looks like there's some sort a bump, or a roll, at the transition of the turns, but there was not. I suspect there are several reasons for it. First, those turns actually steered a little up the hill at the completion, which explains why the skis point uphill slightly in the transition. They are NOT going up a bump.

It is interesting to note, though, that the so-called "virtual bump" phenomenon is also responsible for the appearance of an actual bump. In completed turns, just as in moguls, skis turn downhill and gain speed through the first phase of the turn, then slow down again as they come across and even up the hill. The feet move forward and then back, very much as they do in the "Backpedal" animation shown in the original thread (click here to view).

I suspect that the roughness of the original animation has also caused some of the confusion here. Here's a second attempt, somewhat cleaned up, that I think comes closer to showing what the skiing actually looked like:


Remember that these animations are assembled by hand, from stills extracted from the original video. I had to adjust each frame's size and location on the screen by eye, to make it as smooth as possible, and to make the looped transition point as seamless as I could. The first animation was hastily done. I was a little more careful on the second, and also tried to show some of the actual movement across the hill. Finally, I tilted the images just a little, so they don't actually go uphill at the end of each turn. While this may have involved some artistic license, I think it eliminates the confusing appearance of a bump.

Unfortunately, the original video was only a one-turn clip (where's the rest of the run, Rusty?), so I had very little to work with.

Some notes on carved vs. skidded turns, and the "Slow Line Fast" are in order. As I've often said, I think way too much emphasis is often placed on end results, and way too little on the intent and movements that produce them, causing some of the confusion that has surfaced in this thread. What really matters is the INTENT behind the turns, not the tracks they leave behind, although those tracks will certainly tell much about the effectiveness and character of the skier's movements.

Bode Miller and Hermann Maier often skid several meters off the "pure carved line," especially in an icy downhill course, while a beginner's embryonic and perhaps even defensive first turns will only skid a few inches. Yet few would argue that Miller's and Maier's turns were "skidded type" turns, or that the beginner's turns were carved. It's really much more a question of intent.

Maier and Miller, presumably, were trying to ski their chosen lines, as cleanly and efficiently as possible. They were not trying to "carve," and they certainly weren't trying to skid (except when they are legitimately braking). Their turns are as carved and clean as possible, given the circumstances (speed, radius, steepness, equipment, snow conditions, skill)--but that hardly means they are always "pure carved."

The same is true of the low-speed Basic Parallel turns in my animation. They are "as carved as possible." There is some inevitable skidding, but absolutely no intentional tail-pushing. At the low speed and tight radius, no ski except perhaps a "snowblade" could actually make a pure-carved turn. The animation turns represent the only blend of skills and movements possible to produce them. Tip the skis more, and they would lock up, "rail out," and carve themselves off my chosen line. Tip them any less, and they would lose their grip and skid sideways off the line.

So these turns are heavily steered, necessarily brushed, "as carved as possible," offensive turns meant to demonstrate the movements and skill blend needed to steer a precise, very complete, deliberate line. They represent the "Center Line(TM)," what Weems calls the "Mother Turn." The movements and skill blend match the intent to control LINE, to go (that is, GO!) precisely where I choose to go. As others have noted, they share this intent, and all fundamental movements, with the Wedge Christie, as well as the highly dynamic turns of World Cup GS racers.

They certainly don't represent ALL good skiing. They aren't the only important turns in a good skier's repertoire. They aren't even the most fun type of turns, in my opinion. I've often referred to three very different types of INTENT that dictate nearly all of my skiing. The desire or need to control SPEED dictates braking, intentionally skidded, tail-pushed turns. The desire to control DIRECTION produces the blend shown in the illustration. (And, of course, since direction can control speed, if I choose my line wisely, I minimize the need to control speed, and avoid the ugly, but sometimes useful, braking moves that would result. That is all that is meant by "skiing the slow line fast").) Clearly, different speeds, steepness, condtions, equipment, turn radii, and equipment will change the movements in degree, but not in character. Rotary, edging, and pressure control movements are all blended skillfully as needed, taking full advantage of the ski design and forces available for any particular situation.

The third intent may be the most fun. It's what I do when I don't need to control either speed OR direction, at least not precisely, and I can afford to transfer some, or all, of the control to my skis. It is the intent to CARVE, to tip my skis and let them take me for a great ride, to savor the G-forces that today's skis can produce. For these, I switch off active steering (rotary), tip more, and play with only edge angles and pressure to extract maximum performance from my skis. They're fun. But should my priorities change--either to brake quickly, or to gain more precise control of my line, I'll gladly sacrifice some of that pure carve, as needed.

Finally, FastMan, remember that "anticipation-release" is not itself a unique rotary mechanisim (like classic "rotation," counter-rotation, leg steering, or a blocking pole plant). It is merely a windup-release mechanism that can be involved in ANY mechanism, adding to its power. Classic anticipation-release involved coiling the abdomen and torso (windup) and then releasing the energy to turn the skis. If a firm pole plant is involved, the actual mechanism that turns the skis is the blocking pole plant, acting like a wrench through the extended arm to twist the body and skis. If no pole plant, the mechanism is typically counter-rotation--the "equal and opposite" actions of the upper and lower body rotating in opposite directions. If the anticipation-release is a quick, uninterrupted "1-2" movement, it is classic "rotation."

None of these things, with the possible exception of a VERY small amount of rotation, takes place in the animation. The pole plant is not blocking at all. In fact, I believe what we were actually working on when the video was taken was a "paddling" action of the pole--pulling its tip back as it touches the snow.

Look closely, and you will see that, unlike classic "anticipation-release," there is virtually no twisting in my abdomen or torso, which remain almost entirely square with my pelvis throughout the turns. The "stretch zone" is down in the legs and hip sockets, where the femurs rotate independently. This independent leg rotation, which is fairly active (muscular) in these turns, steers the skis into a slightly countered relationship with the pelvis and upper body, as Rusty has noted. Especially with my very flexible hips, though, there is very little if any windup "coiling spring" effect with this leg rotation, although there is some. And that is, indeed, a form of anticipation-release, although I would suggest that it plays an extremely minor role in the rotary mechanics of these turns.

As Rusty has noted, "pivot slips," as Ric Reiter demonstrates so well in the original animations thread, highlight these leg-rotation movements. Notice the very similar positions that result in both Ric's pivot slips and my short-radius, complete basic parallel turns. The only significant difference is the measured and timely blending in of edging movements to create the desired turn shape!

Well, that's enough for now. Carry on!

Best regards,
Bob Barnes
post #19 of 23
Rusty

Fastman noted ' The tails definitely do not follow the tips in these turns.'

whereas you insist 'What is important to note is the tail of the ski follows the tip of the ski. There is no tail pushing or tail displacement'

It seems to me without carving a path, the ski has to pivot and what we are discussing is the pivoting point...
1/ if the tips are the fixed pivot, the tails move out,
2/ if the tails are fixed the tips move in and
3/ if the foot is fixed both ends rotate around it

Bob's feet do not appear to displace outwards as in a tail push pivoted about the tips, nor do they move inwards so I suspect the feet are themselves pivoting the skis, which might reqire both tail push and tip pull simultaneously as in 3/ above.

As twisting a weighted ski is a No!No!, I suspect this skier is guiding the light inside ski into the turn and with modest tipping of the outside ski, driving that one forward and around from rotation in the hip socket. This is subtlely different from twisting the foot, the thing that gives rotation its bad name.

What I think this discussion highlights is the difficulty in defining the blending of pivoting and edging that goes on in the entire skiing middleground between full carving and pivotslips which do seem so fundamentally different.
post #20 of 23
Thread Starter 
Quote:
Originally posted by daslider:
What I think this discussion highlights is the difficulty in defining the blending of pivoting and edging that goes on in the entire skiing middleground between full carving and pivotslips which do seem so fundamentally different. [/QB]
I think you just described it well!

I like to think in terms of there only being four things you can do to a ski-push, pull, tip, and turn.

One thing I would add to what you wrote above. It is not merely the foot pivoting. As Bob notes, femural rotation is a strong mechanism to turn the ski in pivot slips and in open parallel turns.

For arguments sake call a pivot slip 95% turning, 5% tipping with a blend of flexion and extension.

Open parallel 80% turning 20% tipping or as Bob so aptly describes....as carved as possible.

Carved tips the scales (sorry for the lousy pun) in the opposite direction and weighs in at an arbitrary 95% tipping 5% turning.

The last is the one that befuddles all in so far as they believe in the concept of a "pure carve" involving only tipping the ski on edge. The turning or rotational element derived from the fact that as one knee moves laterally and the other medially the femur rotates.
post #21 of 23
Thread Starter 
Quote:
Originally posted by daslider:
Rusty


1/ if the tips are the fixed pivot, the tails move out,
2/ if the tails are fixed the tips move in and
3/ if the foot is fixed both ends rotate around it

Bob's feet do not appear to displace outwards as in a tail push pivoted about the tips, nor do they move inwards so I suspect the feet are themselves pivoting the skis, which might reqire both tail push and tip pull simultaneously as in 3/ above.

In rereading your post I guess I would pick door #2 without describing the tail as a fixed point.

The tip turns and pulls the tail akin to a tractor trailer (lorrie (sp?) in your case) being pulled in a turn.

I don't recall the guys name, however, I had an interesting discussion with a trainer/PSIA examiner from Aspen this winter. He described the very first movement that they teach to a new skier. They have the student stand in ski boots, lift the toe of one boot an inch or two in the air, leave the heel of the boot on the ground as am pivot point, and ask the student to turn the foot.

Their goal is to never ingrain/demonstrate heel displacement and to emphasise toe turning.
post #22 of 23
Bob Barnes

I have been looking at both loops trying to spot the femural rotation, they are quite hypnotic! What is noticable, moreso in the first one, is an apparent upward tilt of the pelvis at the end of each turn together with a straightening of the torso so that it catches the light for a moment on the coat front, almost like a jetting move.

Are you deliberately driving the outer ski forwards and round and is that what you mean in your description 'This independent leg rotation, which is fairly active (muscular) in these turns, steers the skis into a slightly countered relationship with the pelvis and upper body'?
post #23 of 23
Thread Starter 
Quote:
Originally posted by Bob Barnes/Colorado:

It is interesting to note, though, that the so-called "virtual bump" phenomenon is also responsible for the appearance of an actual bump. In completed turns, just as in moguls, skis turn downhill and gain speed through the first phase of the turn, then slow down again as they come across and even up the hill. The feet move forward and then back, very much as they do in the "Backpedal" animation shown in the original thread (click here to view).
daslider,

I hope Bob checks in, however, in the event he does not, I took the liberty to copy what he wrote earlier, that might start to answer your question.

Mid winter Bob noted that when I made many turns, my outside foot was too far back in the second half of the turn, hence, I levered the front of my boot, resulting in the tail of my outside ski skidding a lot during turn completion.

It was ugly to see on video. I can only describe it as looking like my outside leg sort of lagged behind.It manifested itself in many different types of turns.

To fix the issue, I had to feel as though at the end of many turns, I slid my feet forward about six inches.

The first time we worked on this, as merely a drill, I made turns levered on the back of my boot. A little polarity.

Again, I hope he will check in, however, I feel safe in saying his intent is for his feet to keep moving forward, indeed finishing by moving slightly uphill. and then as the next turn takes place they are drawn back in a manner akin to the backpedal in bumps.
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